In order for plants to grow, they need various resources. For example, plants require light as part of their photosynthesis process. Plant production may be enhanced by addition of supplemental lighting, but this comes at a cost. Similarly, plant production may be enhanced by the addition of supplemental CO2, but this too comes at a cost.
Research has demonstrated that light and CO2 resources can be combined in combinations that optimize plant growth. Examples of such published research are: Both A J, Albright L D, Langhans R W. 1997. Coordinated management of daily PAR integral and carbon dioxide for hydroponic lettuce production. Acta Horticulturae 456:45-51; and Ferentinos K P, Albright L D, Ramani D V. 2000. Optimal light integral and carbon dioxide concentration combinations for lettuce in ventilated greenhouses. J Agric Engng Res, 77(3):309-315. The contents of each reference are incorporated herein by reference in their entirety as a basis for understanding the present invention. Practical application to actual cost efficient greenhouse operation, however, has been lacking, and many greenhouse environmental controllers do not take into account how the plants respond to the environmental conditions over time.
The endless quest of greenhouse operators is to produce the best crops possible at the lowest practical costs. This is an optimization problem in which benefits of a mix of inputs must be balanced against their combined costs. Extant approaches to greenhouse operation have not provided temporally sensitive control strategies to provide optimal combinations of resources in view of varying cost structures associated with at least one of the plant growth resources. As a result, there is a need in the art for control methods and systems that perform such optimizations.
It is known that increasing aerial CO2 concentration (within limits) improves photosynthetic efficiencies of C3 plants. Greenhouse plant production in regions of the world with cloudy climates can benefit from supplemental lighting, particularly during the winter season. Supplemental fighting is typically expensive to operate, whereas CO2 resources are generally inexpensive. However, air infiltration and ventilation are CO2 loss paths potentially making supplemental CO2 more costly than electricity for supplemental lighting in order to achieve comparable growth. Moreover, it is not clear whether the CO2 concentration must remain fixed through time for optimum control and minimum cost. Whether it is cost effective to add CO2, or operate supplemental lighting, and deciding the optimum combination of CO2 concentration and the light integral for the next decision period are important questions that must be answered to implement optimized computer control. Numerous models have been proposed (e.g., Ferentinos. et al., 2000) that explore optimized combinations of the daily light integral and CO2, but generally are not configured for real-time control purposes.
Careful control of the daily growth rate becomes possible when light and CO2 are controlled within tight limits (see Albright, et al. 2000. Controlling greenhouse light to a consistent daily integral. Trans. of the ASAE 43(2):421-431; and see also Both, et al. 2000. Coordinated management of daily PAR integral and carbon dioxide for hydroponic lettuce production. Acta Horticulturae No. 456:45-52; the contents of each reference are incorporated herein by reference.) Coordinated management of the two can substantially increase yields and lower production costs beyond levels achievable with practices based on adding supplemental light only, supplementing CO2 only, supplementing each independently, or simply accepting what the Sun provides.
Thus, a need exists to make cost optimized plant production realizable, particularly through approaches that involve calculating at regular intervals recommended combinations of plant growth resources, such as CO2 concentrations and supplemental lighting, and that translate cost and growth optimized resource combinations into greenhouse resources controller actions.